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Coming advances in coronary artery disease
Drug-eluting stents
Restenosis remains the major drawback to the use of coronary artery stents.
While radiation for in-stent restenosis is a promising approach, there are
drawbacks to this therapy and it doesn’t always work. (Click here for a recent
review of coronary artery radiation therapy.)
Much more useful would be a means of preventing the restenosis in the
first place.
Data presented last week at the ACC meeting only increased the level of enthusiasm for the most promising method of preventing restenosis within stents – drug-eluting stents. Drug-eluting stents are coated with medications that inhibit the tissue growth that causes restenosis. Many drugs can inhibit the growth of cells. While many of them would be considered too risky to administer throughout the entire body, the idea of “delivering” a tiny amount of the drug directly to the tissue that needs to be inhibited is a very attractive one.
The most promising so far are are sirolimus-coated stents and rapamycin-coated stents. Early results suggest that such stents can nearly eliminate the problem of restenosis. If these early results are verified in ongoing trials, drug-eluting stents may revolutionize interventional cardiology. Stenting will suddenly become a more viable option for many patients now being referred for bypass surgery, for instance.
Drug-eluting stents are already a reality. Assuming that current trials will be as favorable as the already-completed clinical trials, these stents should become widely available within 1 – 2 years. (Click here for a recent review of restenosis.)
Non-invasive
diagnosis of coronary artery disease
Both MRI scanning and lesser known techniques such as Multislice Computed
Tomography (MSCT) are on the verge of allowing accurate and reproducible
diagnosis of coronary artery disease without cardiac catheterization.
The technology has all but been solved, and what remains is for the
technology to be refined, and to be made inexpensive enough to allow hospitals
to purchase the equipment in sufficient quantities.
But within a few years, it now finally appears as if diagnosing coronary
artery disease will move into the realm of noninvasive cardiology.
Identifying
vulnerable plaques
Not all coronary artery lesions are equal. Some atherosclerotic plaques are
relatively stable, and relatively unlikely to cause heart attacks.
Other plaques are particularly vulnerable to rupture, which triggers the
clotting phenomenon that produces sudden blockage of the coronary artery and
thus heart attacks.
Unfortunately, when a partial blockage is viewed on a standard heart catheterization, there is no way to distinguish between stable and vulnerable plaques. Therapy, therefore, is directed toward the degree of blockage, and not whether a plaque is actually more prone to rupture. (It is now widely recognized that many heart attacks occur at the sites of “minimal” coronary artery blockages.)
MRI techniques are now being actively developed to help distinguish between stable and vulnerable plaques. This technique will allow doctors to target their therapy (i.e., angioplasty and stents) more effectively to the very lesions that pose the highest risk. (Click here for a recent review of cardiac MRI.)
Angiogenesis
Angiogenesis is the growth of new blood vessels. Scientists have long known that naturally occurring proteins
called Growth Factors (GF) can stimulate blood vessel growth. Early trials have
used infusions of GF into coronary arteries to stimulate new blood vessels in
areas of the heart where the coronary arteries have become blocked.
These trials have been promising.
A new trial reported at the ACC meeting last week described the use of gene therapy to stimulate angiogenesis. The gene (which codes for a form of the GF protein) was delivered to the heart by infusing the gene in an adenovirus “package.” (Viruses are essentially packages of DNA coated with protein. When a virus infects a cell, it uses the cell’s protein factory to “express” the DNA borne by the virus. Thus, the infected cell begins making proteins coded by the viral DNA.) This trial showed that patients receiving the gene therapy showed evidence of significantly improved coronary artery blood flow.
While much work needs to be done to assure the safety and effectiveness of this approach, it is likely that gene therapy to stimulate angiogenesis will become a viable, routine treatment for patients with severe coronary artery disease within the next several years.
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